# Infinite GMRES for parameterized linear systems

We consider linear parameter-dependent systems A(μ) x(μ) = b for many different μ, where A is large and sparse, and depends nonlinearly on μ. Solving such systems individually for each μ would require great computational effort. In this work we propose to compute a partial parameterization x̃≈ x(μ) where x̃(μ) is cheap to compute for many different μ. Our methods are based on the observation that a companion linearization can be formed where the dependence on μ is only linear. In particular, we develop methods which combine the well-established Krylov subspace method for linear systems, GMRES, with algorithms for nonlinear eigenvalue problems (NEPs) to generate a basis for the Krylov subspace. Within this new approach, the basis matrix is constructed in three different ways. We show convergence factor bounds obtained similarly to those for the method GMRES for linear systems. More specifically, a bound is obtained based on the magnitude of the parameter μ and the spectrum of the linear companion matrix, which corresponds to the reciprocal solutions to the corresponding NEP. Numerical experiments illustrate the competitiveness of our methods for large-scale problems.

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